1. Field of the Invention
The invention herein relates to tubular connectors, commonly referred to as "expansion joints," which serve to join the spaced-apart adjacent ends of two sections of air or other gas duct-work.
The use of expansion joints allows for relative movement of the two sections of ductwork in a longitudinal, rotational or lateral direction or simultaneously in any direction. Such expansion joints thus allow for the movement which is due to heating and cooling of ducts, vibration which may occur, and misalignment in duct installation.
2. Description of the Prior Art
Many kinds of expansion joints have been used at one time or another in industrial and commercial installations. Until recently most comprised a fabric section to which were joined metal angle irons forming flanges on the outer extremities of the joint. These metal flanges were attached to corresponding flanges on the adjacent ends of the duct sections to be joined. Typical metal flanged expansion joints have been marketed commercially by the Johns-Manville Corporation under the trade designation of Models "A-250" and "B-500."
The use of such metal flanges increases the weight and complexity of the expansion joint. Consequently, recently there was developed an expansion joint in which the flexible fabric of the joint itself attaches to the flanges of the ductwork, thus simplifying both the construction of the expansion joint and installation, and substantially reducing the weight and expense of the typical expansion joint. These recently developed expansion joints are shown in U.S. Pat. No. 3,647,247 to Pintard and Mollick. Such expansion joints have found considerable success in the marketplace.
The expansion joints described in the aforecited patent have, however, been found to be susceptible to failure at the corners thereof. To overcome this, corner reinforcements, both fabric and metal, have at times been used with such expansion joints. Incorporation of such reinforcements, however, is not desirable for it reduces the expansion joint's advantages by once again increasing the cost of production and adding to the complexity of the finished expansion joint. Further, the use of such reinforcements has not entirely solved the problem of failure of the expansion joints at the corners.